Rack-optimized servers can have severe volumetric constraints resulting from market demand for multiple features and extensive functionality implemented within a chassis with a limited vertical height and limited depth. For example, a chassis is configured to house hard disk drives, Peripheral Component Interconnect (PCI) cards, processors, memory, and others. Chassis depth is commonly defined and limited by cable management constraints. For example, standard 36-inch deep racks may be the maximum allowable in light of bulkiness and/or electromagnetic interference reduction for rack input/output and power cable constraints.
Typically, hard disk drives make electrical and power connection to server electronics via a vertical backplane as shown in FIG. 9A. The arrangement consumes a significant amount of the total available chassis depth due to the alignment of the longest dimension of the hard disk drive with chassis depth. FIGS. 9A and 9B show approximate volumes of two standard versions of hard disk drives used in servers. For example, a conventional four-inch format drive has a longest dimension or length (L4) of 7.3 inches, a width (W4) of 4.3 inches, and a thickness (T4) of 1.05 inches. A conventional 2.5 format drive has a longest dimension or length (L2.5) of 5.9 inches, a width (W2.5) of 3 inches, and a thickness (T2.5) of 0.62 inches. A typical arrangement may have a 0.045 inch gap between drives.
A further difficulty with the conventional vertical backplane arrangement is that the backplane is a solid impediment positioned essentially perpendicular to airflow pathways of cooling fans. Accordingly, the vertical backplane forms a blockage which obstructs airflow, creating a significant airflow resistance.